Twenty Million Americans are reported to be regular users of marijuana, while over 100 million are believed to have used the drug on occasion. However, at this time, when legalizing marijuana is under consideration, almost no data is available on its physiologic effects. Therefore, investigation of possible injury to the lungs' defenses seems merited. The effects of both chronic and short term inhalation of marihuana smoke and of THC injection on pulmonary bacterial susceptibility will be determined by challenging the animals at various intervals post-exposure with a Pseudomonas aeruginosa or a Staphylococcus aureus aerosol and measuring lung bacterial clearance and the number and the phagocytic and intracellular killing capabilities of the alveolar macrophages and the circulating neutrophils. A further in vivo evaluation of the two substances will be made by determining the mortality rate and observing pathologic changes in the lung tissues both before and after aerosol bacterial insults. These studies will provide important data regarding the effects of both short-term and long-term administration of marijuana and THC by injection on pulmonary bacterial susceptibility. It will provide researchers, clinicians and government leaders with vital and necessary information regarding the use of this controversial, yet possibly, beneficial drug.